Studies were continued on the isolation, purification and characterization of biologically active polysaccharides from pneumococci types 6, 9, 10, 21, 22, 29, and 67, Streptococci A, B, F, MG and faecium, Lactobacillus bifidus, micrococcus lysodeikticus, Hydrogenomonas eutrophia, Bacillus subtilis, and polysaccharides from 10 additional ornamental flowers. The polysaccharides were tested for cross reactivity with Type III pneumococcal rabbit and horse antisera. Forsythia and magnolia polysaccharides reacted with low titers to horse antiserum to type III pneumococcus in precipitin tests. Several oligosaccharides from B 512 dextran and type 6 pneumococcus polysaccharide were prepared in addition to complexes of stearoyl, octadecylisocyanate, octadecyliosothiocyanate, and tricarbanilate of B 512 dextran for immunological hapten inhibition in vivo studies. The properties and reactions of the cross reactive polysaccharides may be of considerable interest in the possible role of cross-reactive antigens on immunological reactions.